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Oscilloscope mains safety in the UK

Updated: 22 October 2026

The scope is rechargeable, the title says 400 V or 4,000 V, and the ground clip is already in your hand next to a UK socket or a consumer unit. Oscilloscope mains safety in the UK starts from the opposite fact: a battery and a large voltage in the title are not a measurement category, and none of the six handhelds on the [handheld oscilloscope comparison](/hub/measuring-equipment/oscilloscope-hand) rates that socket. Bandwidth for a hobby signal stays on the [handheld oscilloscope buying guide](/hub/measuring-equipment/oscilloscope-hand/sub/oscilloscope-hand-buying-guide). A safe-board trace stays on [how to use a handheld oscilloscope](/hub/measuring-equipment/oscilloscope-hand/sub/oscilloscope-hand-how-to-use). Peter F. applied HSE notes to these listings on 21 October 2026. A qualifying purchase can earn a commission at no extra cost to you.

The scope is rechargeable, the title says 400 V or 4,000 V, and the ground clip is already in your hand next to a UK socket or a consumer unit.

Our top picks

ZOYI ZOYI ZT-703S

Best overall

ZOYI ZOYI ZT-703S
6.2/10about £86.50
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BSIDE BSIDE OT3

Best value

BSIDE BSIDE OT3
6.8/10about £39.99
View offer
BSIDE BSIDE OT9

Alternative

BSIDE BSIDE OT9
4.8/10about £149.99
View offer
On this page
  1. 1.Why the ground clip is the danger
  2. 2.Category and voltage together
  3. 3.What these listings print
  4. 4.Work law, and the same physics at home

Why the ground clip is the danger

The probe's ground clip is signal common, and HSE's INDG354 says that common is tied to the chassis. Clip it to a live conductor and you short that conductor to the chassis. On a battery handheld there is often no mains earth lead, which does not make the clip safe. Two clips on live and neutral are a short through the case. Neutral is a current-carrying conductor, and it can sit away from earth. INDG354 discourages lifting the earth on a Class I scope, because the case can rise to a dangerous voltage. These listings charge from USB, and the saved listings do not name a BS 1363 charger plug. Battery power does not isolate one channel from the other.

Category and voltage together

A CAT mark is the transient environment, and it is incomplete without a voltage. In Megger's UK explanation, CAT II covers socket outlets and portable equipment, CAT III covers distribution boards and fixed equipment, and CAT IV is the supply side. A voltage with no category does not tell you what the probe will survive. GS38 expects electrician's probes to BS EN 61010-031, with finger barriers and a short exposed tip. A hobby BNC probe is not that lead. UK mains are about 230 V. ±400 V can look larger than that and still say nothing about a transient on a consumer unit.
ZOYI ZOYI ZT-703S

Testsieger

ZOYI ZOYI ZT-703S
6.2/10about £86.50
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What these listings print

Compel's sheet for the OT3 and OT5 family says about ±40 V on x1 and ±400 V on x10. The Amazon bullets say ±400 V and do not add a CAT mark. The OT9 bullet says ±4000 V, with up to 1,000 V DC and 750 V AC on the meter line, and no CAT mark in the file. The ZOYI ZT-703S attribute mentions CAT III 1000 V and CAT IV 600 V. It does not say whether that is the scope BNC or the meter jacks, and the saved file is not the manual. The DSO152 and the O2 state no CAT rating. The O2 mentions 300 V AC and still has no category. None of these six files rates a UK socket or a consumer unit.

Work law, and the same physics at home

The Electricity at Work Regulations 1989, regulation 14, restrict live work where danger may arise. They bind people at work. HSE describes three conditions: it must be unreasonable to do the work dead, it must be reasonable to work live, and suitable precautions must be in place. A householder is not inside that duty in the same way, and the shock physics do not relax. Do not clip these handhelds to a socket circuit or a consumer unit. Two traces are not a differential probe. If you must see a mains waveform, you need a manual that states the category and the voltage for that point, or you leave the cover on and call an electrician.

Common questions

Can I clip the ground lead to mains live?
No. The ground clip is signal common. On the way these scopes are built, that clip is not a second measuring tip. Putting it on live shorts live to the chassis and, if you have a second channel, to the other clip. INDG354 is the HSE note that describes signal common tied to the chassis, and why lifting an earth to float a scope is discouraged.
Does a rechargeable scope float?
The battery removes the mains plug, so there is no earth pin holding the case down. The inputs are still joined to each other unless the manual says each one floats to a stated voltage. None of the six saved listings says that. A floating rating on a Fluke ScopeMeter is a different product, and the numbers do not copy across.
What is CAT III in a UK house?
In Megger's terms, CAT III is distribution and fixed equipment inside the installation, which includes a consumer unit. CAT II is the socket and portable equipment. CAT IV is the supply side. A mark still needs a voltage beside it, such as CAT III 600 V. A pocket scope with no CAT line has not claimed that environment.
Is ±400 V the same as CAT II 300 V?
No. ±400 V on the OT3 and OT5 bullets is a voltage figure. CAT II 300 V is a category plus a voltage, describing transients at a socket. Compel's OT sheet also splits the lower x1 limit at about ±40 V. Without the category on the probe and the instrument, the larger number is not a socket rating.
Does the ZOYI attribute make it safe on a consumer unit?
The attribute names CAT III 1000 V and CAT IV 600 V. It does not say whether that applies to the meter jacks, the scope BNCs, or both, and the saved listing is not a manual. One line on an Amazon specification is not a reason to take the cover off a consumer unit. If the manual for your exact unit does not rate that board, you do not measure it.

Related pages

Oscilloscope for car diagnostics

Handheld oscilloscope

Best pocket oscilloscope: six amazon.co.uk listings

Handheld oscilloscope buying guide: bandwidth first

How to use a handheld oscilloscope on a low voltage

Sources

Public UK sources from the research digest, last checked on 21 October 2026. Shelf prices and star lines are the amazon.co.uk figures captured with these six listings. The price bands are this set, not a market average.

  1. Electricity at Work Regulations 1989, regulation 14 (retrieved 21 October 2026)
  2. HSE GS38: electrical test probes (retrieved 21 October 2026)
  3. HSE INDG354: safety in electrical testing (retrieved 21 October 2026)
  4. Megger: measurement categories (retrieved 21 October 2026)
  5. Keysight: choosing a handheld oscilloscope (retrieved 21 October 2026)
  6. Rohde & Schwarz: oscilloscope buyer's guide (retrieved 21 October 2026)
  7. Compel: OT3 and OT5 handheld oscilloscope (retrieved 21 October 2026)
  8. Pico Automotive: ground clip on a common-ground scope (retrieved 21 October 2026)
  9. amazon.co.uk Lab Oscilloscopes best sellers (retrieved 21 October 2026)